The focus of this project is to establish the beneficial effects of ERK activation on renal cell survival in ischemia reperfusion injury and determine its mechanism of protection following ARF. It has been demonstrated that the Jun-N-terminal Kinases (JNK) and the Extracellularly Regulated Kinases (ERK) members of the Mitogen Activated Protein Kinase family of protein kinases, which are activated after ischemic injury, are determinants of cel fate in a variety of cell stresses. We have shown that ERK is activated in thick ascending limb of the post-ischemic kidney, while JNK is activated in both the proximal tubules and thick ascending limb. As the thick ascending limb cells survive the ischemic insult, we hypothesize that the differences in cell outcome is a result of this difference in the activation of these kinases. We demonstrate that when ERK is inhibited in thick ascending limbs they die, and when activated in PT they survive the oxidant stress. To test the hypothesis that ERK activation is protective against oxidant stress directly, cells will: I) be transfected with a dominant negative ERK cDNA, which should inhibit cell survival in thick ascending limbs; 2) or be transfected with a constitutively active ERK cDNA, which should prove to be just as effective as IGF-1 in protecting proximal cells. In a separate group of experiments we will test the hypothesis that ERK activation inhibits the execution of the death pathways in proximal tubule cells and have designed experiments to pinpoint the precise step at which ERK may supervene in these pathways. Thus, we will first determine the role of endonuclease and caspase activation and the role the mitochondrial permeability transition plays in the activation of these executioners of cell death. We will then proceed to characterize the role that the BCL2 complex of proteins, p21WAF/CIP1, and activation of K-channel activity play in these processes and determine at which site ERK inhibits the cell death pathway. The results of these studies will lay the groundwork for a more targeted approach to the therapy of acute renal damage.